Why the fish died:
Okay, so I myself have a 20g and a 5g with my own Betta, Enrique. Don't worry, he isn't the one who has died. Unfortunately, however, it was my brother's Betta. I'm the one who's actually into fish, my brother was just kind of interested at first but got 'bored'. But, I'm not going to get into how annoyed I am at him, and how a pet is a commitment, and how he should have kept up on the PWCs, etc. This is about the fish.
He had a simlar setup of mine, a 5g heated/filtered, but he pretty much just ended up neglecting the tank by not doing a water change for like 3+ weeks. I didn't know that he forgot to clean the tank, I just assumed he had been keeping up on maintenance. Well, the Betta got Dropsy. When I discovered this I immediately did a 50% water change and dosed the tank with Maracyn 2 that I had extra of. That kept him alive overnight. The next night he was still breathing but didn't look like he would make it, but still I dosed the tank again with the medication. By the following day, he was dead. I was really upset.
Now I have an empty tank and would like to add a new Betta to it without having to re-cycle the tank. Obviously this would not be in the care of my incapable brother, but for me.
What I then did to the tank:
I took about half the water out and put it into a separate bucket. I then took all the decor out and put it into that bucket of tank water. This was so that the decor had somewhere where it could stay wet so the bacteria wouldn't die off while I took out the rest of the tank water. I then vacuumed the gravel and continued to drain the tank of water until it was juuuust
above the gravel. I filled the tank back with fresh, de-chlorinated water and put the decor back in, too.
Tomorrow morning I plan to test the water to be sure all the levels are good.
So, am I doing this right? I did a 100% water change to get rid of the water in which a fish had been dying. But is it safe to add a new Betta? All I changed was the water so I shouldn't have to re-cycle. But I'm sure there are traces of the Maracyn 2 left in the filter media, would that be harmful? Also, it isn't like Dropsy-bacteria can linger in the tank, right?
Help is appreciated. Thank you!